1. Field of the Invention
The present invention relates to an optical recording medium comprising a recording layer which is capable of writing information therein, reading written information therefrom, and rewriting written information therein. The present invention also relates to a recording material for use in the recording layer of the optical recording medium.
The present invention also relates to a method of producing the optical recording medium.
The present invention also relates to a method of writing information in the optical recording medium, reading written information therefrom, and rewriting written information therein.
2. Discussion of Background
As an optical recording medium capable of writing information therein, reading written information therefrom, and rewriting written information therein, with a light beam irradiation, there is well known a phase-change optical recording medium, which utilizes the reversible phase changes between a crystalline phase and an amorphous phase thereof.
The inventors of the present invention have studied phase-change optical recording media, in which an Sb—Te recording material and an Ag—In—Sb—Te recording material are used, and have discovered that the phase-change optical recording media using these recording materials have excellent characteristics, for example, in terms of C/N, erasing ratio, sensitivity, jittering, preservation stability, repeated writing and reading stability (hereinafter referred to as reading optical stability).
Attention has been paid to the recent trend that the optical recording media are being developed into DVD media. In comparison with conventional CD media, the DVD media have a larger capacity, so that it is required that the response or correspondence to recording linear velocity (hereinafter referred to as the correspondence to recording linear velocity) be higher and that the beam spot on a drive side be small.
As the conventionally proposed Sb—Te recording material and Ag—In—Sb—Te recording material, there have been employed materials with such a composition that can secure the preservation stability and the reading optical stability.
When attention is paid to Sb and Te of the constituent elements of the above-mentioned recording materials, the compositions in the shade area in the graph in FIG. 1 are used in the conventional CD media, in which graph the composition data are plotted with the recording linear velocity and the preservation stability (both with an arbitrary unit) as ordinate and Sb/(Sb+Te) as abscissa.
Such media have the problems that when the recording linear velocity is increased, the preservation stability and the reading optical stability deteriorate, and that when recording density is increased by reducing the size of the beam spot on the side of the drive, a sufficient sensitivity for use in practice cannot be obtained.